1. Field of Invention
This invention relates to acid digestion and simultaneous catalytic chemical conversion of cellulose materials to ethanol at high yields in a single process step. Specifically, this application discloses efficient catalytic conversion of cellulose materials including prairie grass, switch grass, bagasse, wood fiber, wood sawdust, news paper, cotton, waste cellulose products and starch materials in an acid digestion solvent to ethanol employing catalysts based on transition metal complexes possessing a degree of symmetry as described herein.
2. Description of Prior Art
The chemical process industry has grown to maturity based on petroleum feed stocks, a non-renewable resource that may become unavailable in the next 100 years. This planet Earth fosters continual growth of abundant carbohydrate based plants including fruits, vegetables, starches, grain food sources, grasses, cotton, shrubs, trees and related natural waste materials. Grains, corn cobs, the support plant stalks and certain grasses are, in part, subject to bio-fermentation processes producing ethanol and related products at modest yields. These processes are slow, require significant nutrients for plant growth and convert some ten percent of the cellulose and related materials to ethanol. A major industry is blooming in ethanol production and this application teaches rapid, efficient catalytic conversion of essentially all cellulose and starch materials to ethanol for use as a fuel and a raw material in the chemical process industry.
A number of process paths have previously been taught for chemical conversion of cellulose and hemi-cellulose materials to ethanol. These processes include fermentation of grains, corn and corn cobs, dilute acid pre-treatment or acidic steam treatment of dried plant materials followed by fermentation of the resulting sugars, enzymatic digestion of cellulose to hemicelluloses and sugars for fermentation as well as gasification of wood chips to carbon monoxide and hydrogen (synthesis gas) to produce products by Fischer-Tropsch type processes. Gasification is expensive and requires some 300° C. to 600° C. in an inert gas environment, acidic steam treatment subjects bio-mass to pressure with temperatures up to 180° C., acid digestion or hydrolysis can be conducted at temperatures of 20° C. to 120° C. while fermentation may be operated in the 20° C. to 55° C. range. Ethanol has been made from ethylene dissolved in sulfuric acid, diluted and isolated by distillation. It has also been produced by heating ethylene with steam at 300° C. and 1000 to 4000 psi pressure using acid or acidic transition metal oxide catalysts. U.S. Pat. No. 4,415,749, issued Nov. 15, 1983, teaches a process for production of ethanol and methyl acetate in the vapor phase at 225° C. to 300° C. over zero valent Rh and Fe at 50 psig to 250 psig pressure. U.S. Pat. No. 6,747,067, issued Jun. 8, 2004, teaches gasification of cellulose to carbon monoxide and hydrogen for subsequent formation of methanol, ethanol and related products.
There are a number of dilute acid digestion or pre-treatment process disclosed for partial conversion of cellulose to sugars for subsequent formation of ethanol by fermentation. U.S. Pat. No. 6,660,506, issued Dec. 9, 2003, teaches dilute acid hydrolysis of cellulose, with metal salts, for partial conversion to sugars. U.S. Pat. No. 7,198,925, issued Apr. 3, 2007, teaches acidic steam pretreatment of bale quantities of cereal straw, stover or grass for hydrolysis of hemicellulose to xylose at 160° C. to 280° C.
The present application discloses use of low valent mono-metal, di-metal, tri-metal and/or poly-metal backbone or molecular string type transition metal catalysts, as described in this application, for direct production of high yields of ethanol from cellulose. Ethanol production occurs in both open and sealed reactors but product yields are higher for the sealed reactor process.